Submitted by sandhyagir on Fri, 23/10/2009 - 11:58
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| Striga spp. are root parasites of cereals and legumes. They cause serious economic losses to a range of host plants, primarily sorghum and pearl millet. Although more than 60 species have been described in the genus Striga, only seven are considered economically important: S. hermonthica, S. asiatica, S. densiflora, S. euphrasioides, S. aspera, S. forbesii (all specific to cereals); and S. gesnerioides (specific to dicots). Breeding genotypes resistant to Striga is recognized as the most economic way to avert the losses caused by Striga. Precise and reliable screening techniques are indispensable prerequisites in breeding for resistance to any yield reducer. In the case of the parasitic weed Striga, the establishment on a host root and its subsequent emergence are influenced by complex interactions between the Striga, the host, and edaphic and atmospheric environmental factors. The development and use of efficient screening systems in Striga resistance breeding has been slow, but with the increasing urgency to alleviate Striga-caused losses all over the semi-arid world, there has been increased emphasis on breeding Striga-resistant sorghum and millet varieties. Accompanying this breeding work is an increased need to develop efficient resistance screening systems. This publication describes the prevailing screening systems and discusses their usefulness. Influence of the host root in determining the fate of the parasite's establishment occurs in three developmental stages of the parasite: seed germination, haustorial establishment, and subsequent growth and reproduction of the Striga plant. Low stimulant production, mechanical barriers, and antibiosis h ave been identified as mechanisms conferring Striga resistance in sorghum. The latter two were termed anti-haustorial factors (Saunders 1933, 1942). To determine host resistance, researchers have adopted either of two approaches: screening for an individual mechanism (primarily in the laboratory), or screening for low emergence frequency of Striga plants, which may involve one or more resistance mechanisms (mostly in the field). |  |
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